May 2009 Newsletter

CAS Newsletter May 2009


New ! Buy your CAS BACnet Explorer from Engenuity.


Starting June 2008, you can buy the CAS BACnet Explorer from Engenuity Systems. You may already know Engenuity for their LonWorks products – but did you know they have expanded their scope when it comes to open systems products such as BACnet?

Founded in 1994, Engenuity Systems, Inc. based in Chandler, Arizona began as a manufacturer focusing on contracted engineering and the development of LonWorks® interface cards, I/O products and drivers. As the company grew, it realized a need to provide customers with an effective way to purchase LonWorks® – based products worldwide. Engenuity currently offers more than 20,000 products from over 100 manufacturers for use in building automation networks, specializing in devices utilizing LonWorks® technology, a leading networking and communication standard; and various wireless technologies that extend the reach of control networks and applications for controllers, sensors, actuators and other devices.

CAS Welcomes a new engineer – Johan Jacobs

Johan Jacobs joined CAS at the beginning of May. His primary focus will be embedded systems and Bacnet software development.

After his studies Johan started his career with Denel Aerospace Systems. They specialize in the development of guided weapon systems (eg. missiles). He worked on the A-Darter project which is the development of a new 5th generation air-to-air missile. Most of his work involved schematic design as well as PCB design. He was responsible for the four PCB’s which are located in the front gimbal of the missile, while under the supervision of his mentor. Johan had to write embedded C test software for the validation of our first prototype PCB’s and was also responsible for some of the documentation and design reviews. While he worked at Denel he also had the chance to attend a few courses on VHDL programming as well as hardware designing for EMI/EMC and one or two other courses.

GE Total Lighting Control (TLC)

Do you need to integrate TLC systems into BACnet, Lonworks or some other systems ? We have proven solutions. CAS have a FieldServer driver capable of connecting GE-TLC systems to over 110 other protocols. Our solutions include an option which allows you to connect your GE configuration computer via the FieldServer, sharing the connection to the TLC panels.

The dangers of XML for System Intergators

Just because a system has an XML interface does not mean you can use it. There are some very important questions you must ask in evaluating the usefulness of an XML interface.

XML provides a syntax and structure but imposes no obligation on how it must be used.

Consider the example of spoken language. English imposes rules on syntax and structure but does not oblige you to say anything useful or comprehensible to other people.

Data Transfer using English

  • “Give me the data!” is a valid instruction in English
  • “Please email me the 2007 sales figures, grouped by territory with a monthly breakdown in tabular format” is also a valid instruction.

Your assistant is likely to respond well to the 2nd instruction and not know how to respond to the first.

The same considerations apply to XML. Now consider an XML example:

Data Transfer using XML

Format example


< poll >
       < source >
		< nodeId > 22 < /nodeId >
		< dest >
			< nodeId > 11
                        < /nodeId >
			< nodeName > node_A
                        < /nodeName >
		< /dest >
	< responseRequirement > dataOnly
        < /responseRequirement >
	< query >
		< action > read < /action >
		< tableName > Setpoints
                < /tableName >
			< address > 10
                        < /address >
			< length > 3
                        < /length >
	< /query >
< /poll >

Its not hard to see that the success of the query is dependent on the ability of the system to understand the query. Just because it complies with the rules of the XML syntax does not mean the interface will understand it.

Here are some key questions to ask:

1. Is the XML interface implemented using TCP/IP or UDP?

2. What is the XML Schema? The schema provides the structure of the XML packets used to query and respond with system data. It shows how the messages must be formatted and defines the data types of the various message fields (in the world or protocols the schema is equivalent to the protocol specification).

3. All the other normal questions you would ask of an interface – What data is available? How much can be transferred at once? What is the scaling? How are data objects addressed? etc…

Ethernet Cables – Cat5 and Cat5e

Where do the terms Cat5 and Cat5e come from?

TIA Telecommunications Industry Association, TIA defined standard TIA-568-B which defines the cables and structured or modular cabling systems and termination standards for building and telecom cabling systems.
Cat5 and Cat5e Cable’s What is the difference?

  • Very simply put: The 5e cable is tested to a higher standard. A manufacturer may produce a single cable and only test some of it to the 5e standard. The physical characteristics of the cable are no different but the Cat5e’s higher specification makes it suitable for Gigabit Ethernet.
  • Whilst we are on the subject what about Cat6 ? Bandwidth is 2.5 greater at 250MhZ and that’s probably the limit with RJ45 connectors. You might be future proofing using this cable but you could also be wasting money. Also remember that Cat6 is a high tech cable and requires connectors and patch cables assembled to meet the standard.
Category 5 Category 5e
Frequency 100 MHz 100 MHz
Attenuation (Min. at 100 MHz) 22 dB 22 dB
Characteristic Impedance 100 ohms ± 15% 100 ohms ± 15%
NEXT (Min. at 100 MHz) 32.3 dB 35.3 dB
PS-NEXT (Min. at 100 MHz) no specification 32.3 dB
ELFEXT (Min. at 100 MHz) no specification 23.8 dB
PS-ELFEXT (Min. at 100 MHz) no specification 20.8 dB
Return Loss (Min. at 100 MHz) 16.0 dB 20.1 dB
Delay Skew (Max. per 100 m) no specification 45 ns

Ethernet Cable Color Coding
There are two color coding standards. The color coding standard does not affect whether the cable is a cross-over or straight through patch cable. Color does not affect performance or use of the cable.

Standard 568A Standard 568B
This is the most commonly used for patch cables.
1 White-Green 1 White-Orange
2 Green 2 Orange
3< White-Orange 3 White-Green
4 Blue 4 Blue
55 White-Blue 5 White-Blue
6 Orange 6 Green
7 White-Brown 7 White-Brown
8 Brown 8 Brown

BACnet School


Flavor Application Affects you?
  • Uses the TCP/IP protocol
  • Controller to contoller
  • Controller to HMI
  • Some field devices
On the up
Ethernet 802.3
  • Raw Ethernet Packets
Being displaced by IP
Point to Point
  • Modems and phone lines
Rare. Expected to disappear.
  • Field devices
Millions of installed devices.

This article can be found here.


Data inside a BACnet device is organized as a series of objects. Each object has a type and a set of properties. There is always at least one object in a device – it is used to represent the device itself . The other objects represent the device’s data.

In practical terms think of a simple thermostat. Our example is a simple device that has a temperature sensor, allows the set point to be changed locally or remotely, has a local remote selection and reports there is an internal fault by reporting its status as normal/abnormal.


Commonly used properties

Object Type:
Popular Object Types: Analog Input, Analog Output, Binary Input, Binary Output.

Instance Number:
A number that must be not be repeated for any other object of the same type.


Present Value:
The current value of the object. BACnet has ways of telling you if the present value is valid – it uses a property called ‘Reliability’.
This article can be found here.



2008 Chipkin Automation Systems –
BACnet is a registered trademark of ASHRAE.
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